Reflector for rectilinear light sources



Oct. 19, 1937. 5 2,096,453

REFLECTOR FOR RECTILINEAR LIGHT SOURCES Filed June 27. 1934 INVENIOR..Maurz'ce Exelmans.

WMAJ A TTORNEYI Patented Oct. 19, 1937 UNITED STATES PATENT OFFICEREFLECTOR FOR RECTILINEAR LIGHT SOURCES Maurice Exelmans, Paris, France,

liolophane Company, Inc.,

asslgnor to New York, N. Y., a

In France 7 Claims.

The present invention relates to reflectors for rectilinear lightsources.

The divergence of light rays reflected from a point on a reflector is afunction of the size of the light source. Where point, or substantiallypoint, light sources are employed the divergence of the reflected lightis comparatively small and may serve to improve the diffusion of thelight without seriously impairing the control of the dominant light intothe desired direction. Where long light sources are employed, divergenceof the reflected light in longitudinal planes is substantial, dependingupon the length of the light source and its distance from the point onthe reflecting surface under consideration. The minimum angie ofdivergence in such longitudinal planes is obtained at a point where thenormal to the reflecting surface intersects the center of the long lightsource. Long reflecting troughs such as ordinarily used with long lightsources have been found unsatisfactory. especially when one desires toavoid spreading the light through wide angles longitudinal of the longlighting unit.

According to the present invention the reflector they may be made inmolds capable of manufacture by ordinary machining operations.

Other and further objects of the invention will appear as thedescription proceeds.

The accompanying drawing shows, for purposes of illustrating the presentinvention, two of the many possible embodiments in which the inventionmay take form, it being understood that the drawing is illustrative ofthe invention rather than limiting the same. In the drawing:

Fig. 1 is a transverse sectional view through a prismatic cylindricalreflector in a plane perpendicular to the source showing the control ofthe rays in this perpendicular plane;

Fig. 2 is a longitudinal sectional view in a plane parallel to thesource showing the control of the rays in this plane; and

Figs. 3 and 4 are sectional views in planes respectively perpendicularto and parallel to the source showing a'modifled form of reflectorgiving control in these two planes.

The reflector form it of Figures 1 and 2 is made of pressed glass andexternally silvered as indicated at ii. It is of semicylindrical shapeslightis so designed that divergence of light in longi- July 3, 1933 lytapered if desired. Qne. surface of the reflector form is stepped'toform longitudinally extending prisms as indicated at !2 in Figure 1,while the other surface is stepped to form a series of prisms l3extending in transverse planes. The longitudinal prisms preferablyextend the entire length of the reflector form, while the transverseprisms are generally placed on the part of the reflector form whichextends beyond the light source and are omitted from the part oppositethe light source. Where the longitudinal prisms cover only the part ofthe reflector form opposite the light source, the annular andlongitudinal prisms may be on the same surface of the glass.

When, as in Fig. 1, the rectilinear source S is disposed parallel withand above the center or axis 0, rays, such as SI emitted in the plane ofthe figure would, in the absence of prisms be reflected symmetrically toCI along the line IR. These rays would cross and diverge widely. Tosecure a light distribution having less spread. the prisms [2 areemployed. The light will then emerge in a direction such as indicated atIR. These light rays are more nearly parallel.

The prisms l2 will not be effective, of course, to any great extentexcept in the case of rays perpendicular to the source; it will diminishaccording to the deviation from that direction; it will disappear inplanes parallel to the source.

The prisms i3 shown in Fig. 2 are especially adapted to control thedistribution in planes parallel to the source. In this case the naturaldivergence would be exaggerated by a non-prismatic reflector form and isreduced by the prisms. The rays of greatest divergence in longitudinalplanes are those emitted by the extreme points S1 and S2. The point A isopposite the mid-point of the source S, so that rays 81A and 82A havingan angle of incidence a give the smallest divergence. A ray such as SzJwould, in the absence of prisms, reflect normally in direction JR. If atthis point a prism i8 is placed so that the ray JR is reflected indirection JR parallel to A81. all the rays falling at this point will bereflected within angle a, which will thus be a measure of the maximumangle of divergence of the reflected beam. The other extreme ray SIJwill be, for example, reflected in direction JRi.

A reflector comprising both the system of prisms of Fig. 1 and those inFig. 2 thus permits a control of the distribution in two perpendicularplanes.

The molds for making the reflector form may be made by ordinarymachining processes. The prisms i3 are surfaces of revolution about theaxes parallel to A8 and A32.

center C and hence the mold parts for forming them may be turned in alathe. The prisms l2 are straight and the mold parts for forming themmay be formed by planing.

Figs. 3 and 4 illustrate the case of a reflector or form I silvered asindicated at l5 and provided with prisms l6 modifying the distributionin the perpendicular plane to the source, and of which the longitudinalsections have special curvature determined in the function of 'thedesired distribution.

The profile in the plane passing along the source S may be, for-example,formed by two parabolic elements having their foci respectively at theends S1 and S2 of the filament and their In effect, as ,before, theleast divergencethat one can obtain is divergence 2a. For a ray such asS21, we will have in the case of a reflecting cylinder a reflected rayI'R very divergent. In giving to the corresponding mirrored portion aparabolic form with focus at S2 and axis parallel to ASi, the ray S21will be reflected according to direction IR parallel to ASi, all theother reflected rays being included in this angle of divergence.

The reflector thus constructed will, therefore, be of circular sectionin transverse planes and of parabolic section in longitudinal-planes:and will have prisms disposed parallel to the source. The mold can bemechanically turned and the prisms cut on a lathe.

It is obvious that the invention may be embodied in many forms andconstructions within the scope of the claims, and I wish it to beunderstood that the particular forms shown are but a few of the twoforms. Various modifications and changes being possible, I do nototherwise limit myself in any way with respect thereto.

Whatis claimed is:

1. In a luminair, the combination with a long light source of atrough-shaped reflector composed of a light refracting medium externallymirrored and in which the light source is longitudinally disposed, saidlight source being positioned within the reflector so that lines drawnfrom its center and an end thereof to the vertex center of the reflectormake an angle a, the.

light refractlng medium having longitudinally extending prisms whichincrease the angle of reflected light relative to the normal to theprofile to decrease the concentration of light reflected in transverseplanes, the reflector also having a conformation which decreases thespread of reflected light in longitudinal planes and forms suchreflected light into a beam moderately divergent in longitudinal planes,the conformation of the lateral end portions of the reflector being suchthat a ray of light reflected by said end portions will make \with aline parallel to the line joining the centers of the light source andreflector an angle not greater than angle a, the ends of the reflectorbeing open to allow the escape of said moderately divergent beam.

2. In a luminair, thecombination with a. long light source of atrough-shaped reflector composed of a light retracting medium externallymirrored and in which the light source is longitudinally disposed, thelight refracting medium having longitudinally extending prisms whichincrease the angle of reflected'light relative to the normal to theprofile to decrease the concentration of light reflected in transverseplanes,

the light retracting medium having transverse prisms which reduce theangle of the reflected light relative to the normal to the longitudinalprofile of the reflector and form such reflected light into a beammoderately divergent in longitudinal planes, the ends of the reflectorbeing open to allow the escape of said moderately divergent beam.

3. In a luminalr, the combination with a. long light source of atrough-shaped reflector com posed of a light refractlng mediumextemallymirrored and in which the light source is longitudinallydisposed, the light refracting medium having longitudinally extendingprisms which increase the angle of reflected light relative to thenormal to the profile to decrease the concentration or light reflectedin transverse planes, the light refracting medium havingintemallydisposed transverse prisms which reduce the angle of the reflected lightrelative to the normal to the longitudinal profile of the reflector andform such reflected light into a beam moderately divergent inlongitudinal planes, the ends of the reflector being open to allow theescape of said moderately divergent beam.

4. In a luminair, the combination with a long light source of anexternally-mirrored, troughshaped prismatic reflector in which the lightsource is longitudinally disposed, the reflector being ,of substantiallysemi-circular transverse profile and provided on one surface withlongitudinally extending ridges out of parallelism with the opposed.surface and disposed to increase the angle of emission of the reflectedlight relative to" the normal to the profile of the reflector, wherebylight radiated in transverse planes is decreased in divergence, the endsof the reflector having semi-circular prisms in transverse planes.

5. In a luminair, the combination with a long light source of anexternally-mirrored, troughshaped prismatic reflector in which the lightsource is longitudinally disposed, the reflector being of substantiallysemi-circular transverse profile and provided on one surface withlongitudinally extending ridges out of parallelism with the opposedsurface and disposed to increase the angle of emission of .the reflectedlight relative to the normal to the profile of thereflector, wherebylight radiated in transverse planes is decreased in divergence, the endsof the reflector having semi-circular prisms in transverse planes andplaced on the surface of the reflector opposite that which carries thelongitudinal prisms.

6. A reflector for long light sources comprising an externally-mirrored,trough-shaped prismatic reflector form having longitudinally extendingprisms and adjacent its ends transverse prisms.

'7. In a luminair, the combination with a long light source, of atrough-shaped reflector comprising an externally mirrored lightrefractor, the reflector being of semi-circular cross section intransverse planes and having longitudinally extending prisms parallelwith the light source, the trough being longer than the light source andhaving a cross section in longitudinal planes composed of two parabolicelements each having a focus at the opposite end of the light source andan axis parallel to the rays of minimum divergence.

MAURICE EXELMANS.

